A plasma processing apparatus engaged in an etching process or a film forming process executed on a semiconductor wafer (hereafter may be simply referred to as a “wafer”) with high-density plasma generated in a relatively low pressure environment is usually used in a semiconductor device manufacturing process. In a plane parallel plasma processing apparatus, for instance, a radio-frequency electrical field is formed between a pair of plane parallel electrodes (an upper electrode and a lower electrode) disposed within a processing chamber by delivering a processing gas into the processing chamber and supplying radio-frequency power to one of or both of the electrodes from an RF generator. Plasma is generated from the processing gas via the radio-frequency electrical field and the plasma thus generated is used in the specific type of processing executed on the wafer, such as etching or film formation.
A matcher that matches the input impedance at an electrode and the output impedance at the RF generator is disposed between the RF generator and the electrode. Via the matcher, the extent of reflection of the radio-frequency at the electrode can be minimized so as to ensure that plasma is efficiently generated within the processing chamber.
The power level, the voltage, the current and the load impedance (plasma impedance) of the radio-frequency power supplied to the electrode in such a plasma processing apparatus reflect the state of plasma generated within the processing chamber. Accordingly, by adjusting apparatus control parameters (hereafter referred to as “plasma parameters”) related to the plasma generation based upon these electrical characteristics, the plasma generated within the processing chamber can be optimized and stabilized.
The plasma processing apparatus thus normally includes a probe disposed between the RF generator and the electrode, which is used to measure the electrical characteristics of the radio-frequency power supplied to the electrode, such as the radio-frequency current or the radio-frequency voltage (see, for instance, patent reference literature 1 below). The control device in this type of plasma processing apparatus is equipped with a data analyzing unit that analyzes voltage data or current data provided through the probe measurement. The data analyzing unit uses the measurement data provided from the probe to calculate, for instance, the time characteristics of the radio-frequency voltage and the radio-frequency current, the sizes of the radio-frequency power traveling wave and the reflected wave, the effective radio-frequency power, the load impedance and the like. Based upon the calculation results, the control unit adjusts the plasma parameters such as the flow rate of the processing gas delivered into the processing chamber, the degree of vacuum within the processing chamber, the level of the radio-frequency power output from the RF generator and the level of the capacitive reactance component at the matcher. Plasma optimized for the production processing conditions can be thus formed inside the processing chamber.
The plasma processing apparatus in the related art is normally fitted with a compact all-purpose probe unit provided as a unit separate from the plasma processing apparatus itself. In order to assure ease of mounting operation and efficient use of installation space, the probe unit may be housed inside the casing of the matcher by cutting off the radio-frequency transmission path within the circuit installed in the matcher. As an alternative, the probe unit may be mounted outside the matcher by inserting the probe unit in the radio-frequency transmission path (e.g., a coaxial cable or a feeder rod adopting an enclosed tube structure) connecting the matcher with the plasma processing apparatus (see patent reference literatures 1 and 2 below). In either case, the probe unit may be disposed between two separate segments of the radio-frequency transmission path or the probe unit may be disposed at a separate connector member used to connect the radio-frequency transmission path.    (Patent Reference Literature 1)    Japanese Laid Open Patent Publication No. 2005-123578 corresponding to U.S. Patent Publication No. 2005/0095732 A1    (Patent Reference Literature 2)    Japanese Laid Open Patent Publication No. 10-185960
Today, as ever higher levels of integration in semiconductor devices are pursued, increasingly fine circuit patterns are required in semiconductor devices. This necessitates extremely rigorous control to meet the required machining dimensional accuracy. In some applications, high-density plasma is generated in a lower pressure environment with radio-frequency power with a higher frequency supplied to the electrode inside the processing chamber to assure the required level of dimensional accuracy in finer circuit patterns.
However, as the frequency of the radio-frequency power supplied to the electrode increases, the state of the plasma formed inside the processing chamber becomes more susceptible to fluctuations attributable to the inductive reactance component at, for instance, a copper plate connecting components, a feeder rod connecting the matcher with the electrode or the like. This means that today more than ever, with the frequency of the radio-frequency power becoming even higher, it is crucial to measure the electrical characteristics of the radio-frequency power with better accuracy and adjust the plasma parameters with a higher level of precision.
It is essential that the measurement system including the probe be calibrated with a high level of accuracy to assure better accuracy in the measurement of the electrical characteristics of the radio-frequency power. Since it is difficult to calibrate the measurement system while it is actually connected to the plasma processing apparatus, the measurement system should be preferably calibrated before installing the probe unit at the plasma processing apparatus by creating a simulation environment simulating the electrical characteristics of the actual plasma processing apparatus and installing the probe unit alone in the simulation environment.
However, since the probe unit in the related art, provided as a separate entity from the radio-frequency transmission path, is disposed in the middle of the radio-frequency transmission path as described earlier, the electrical characteristics measured via the probe unit are bound to be affected by the mounting position at which the probe unit is mounted at the plasma processing apparatus. In other words, while the measurement system may be calibrated rigorously in the simulation environment created in conjunction with the probe unit alone, there still may be an error in a value measured via the probe unit mounted at the actual plasma processing apparatus. Furthermore, the extent of the error is bound to vary among individual plasma processing apparatuses. Depending upon the extent of the error in the measurement value, the corresponding plasma parameters may not be accurately adjusted and ultimately, the plasma may not be held in a desirable, stable state.
In addition, when the probe unit is inserted between two separate segments of the radio-frequency transmission path, as in the related art, the probe unit itself becomes a load component in the radio-frequency circuit, giving rise to a concern that power loss may occur at the insertion position. Furthermore, contact resistance, which is bound to occur at the position where the probe unit is connected, may also result in power loss. Under such circumstances, the radio-frequency power output from the RF generator will be greatly attenuated through the transmission path and, if the radio-frequency power supplied to the electrode is insufficient, plasma in the desired state will not be generated.
The radio-frequency transmission path is normally constituted with a transmission line assuming a co-axial structure such as a co-axial cable or a radio-frequency transmission line with a double-pipe structure. As the probe unit in the related art is inserted at such a co-axial transmission line, an error such as a probe unit mounting error or a mounting error with regard to the connector member used to mount the probe unit is bound to occur, making it very difficult to maintain a high precision co-axial structure. Such mounting errors and the like are likely to greatly alter the electrical characteristics in the transmission line.
Moreover, a probe unit housed inside the casing of the matcher, as described earlier, will need to be replaced when the matcher itself is replaced for maintenance or the like. It is more likely that measurement data continuity will be lost when the measurement of the electrical characteristics of the radio-frequency power is resumed following the matcher replacement. Such a loss of measurement data continuity gives rise to a concern that the quality of plasma generated after the matcher replacement may be different from that prior to the matcher replacement.
An object of the present invention, having been completed by addressing the issues discussed above, is to provide a plasma processing apparatus and a feeder rod used therein, with which the extent of power loss resulting from the probe installation can be greatly reduced, the inconsistency among measurement values obtained from various apparatuses, attributable to the probe mounting error, can be prevented and the probe measurement system can be calibrated with the probe assuming the mounted state in which it is actually engaged in operation, so as to ensure that the electrical characteristics of the radio-frequency power can be measured with a higher level of accuracy over the related art.